This application relates to a unique laboratory pressure vessel or autoclave especially suitable for laboratory experimentation. The laboratory pressure vessel provides a wide variety of programmable conditions of use, for example, pressures up to 2,000 psi, temperatures up to 450.degree. F. (230.degree. C.) and agitation at speeds up to 3000 rpm. Pressure, temperature and agitation conditions are variables that affect the rate and nature of most chemical reactions. Thus the unique autoclave described herein is especially suitable for laboratory study of chemical processes and the optimization thereof. It is a feature of the autoclave according to this invention that it is easily assembled and disassembled and easily accessed for setting up the next run and/or cleaning up after a run. It is unnecessary to disconnect pressure conduit, thermowell connections, and agitating devices in order to open the vessel. Further, laborious bolting and unbolting of the cover and the body are unnecessary.